Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Mimicking Gen3 Prius Exhaust Heat Recovery

Rokeby · 12-19-2009, 08:20 AM

Piwoslaw,

A very interesting thread that is bump-worthy.

A Prius driver seriously interested in keeping MPGs up in the colder months
soon comes to understand that in large part any efforts will hinge on
retaining heat in the ICE and catalytic converter. Getting to the most
efficient operating regime, S4, depends on getting the two up to temp, and
in stop and go driving at least, the HSD computers will restart the ICE as it
needs to keep temps up whether you like it or not. Thinking about any heat
(= fuel = $$) that leaks off into the cold, cruel world is frustrating.

There are a number of threads here on passive ways to retain what little
heat the ICE puts off: grill blocks, pre-start-up block heaters, engine
blankets, etc. All good stuff. Still, sitting at a traffic stop in the windy cold,
ICE-off, with the block temps dropping rapidly (ScanGauge readout), I see
the ICE kicking on apparently only to warm up the ICE or CC arbitrarily at
~145 degF, ~135 degF, and always if temps get as low as 110 degF. You
wonder, Where the heck did all the BTUs go? Out the proverbial window of
course.

Back on target:

Here is a link to some pictures of the GEN III exhaust heat recovery
hardware. (Thank you, Bob Wilson.) Not great, but a start:

Detroit Auto Show and Prius 2010

A little farther afield, here is a plan to recover Prius exhaust heat with a
small steam turbine generator:

Steam-Hybrid Prius

I see that this system is "total loss" as regards the water/steam. It ends up
going out the exhaust pipe. I wonder what the MPGs are for the water.

And finally, a proposal published in Dec. 2007 to use "theromelectrics" to
turn the excess exhaust heat directly into electricity.

http://www.nrel.gov/docs/fy08osti/42256.pdf

"Identifying an optimal system size is challenging. Sufficient waste heat is
available at highway speeds, but little is available in city driving where the effect of engine start-stop cycles is expected to reduce waste heat by 30%. As a compromise, this study sized TE generators based on the amount of waste heat available at 40 mph (64 km/hr) constant speed driving. In transient simulations, these systems were slightly undersized to capture peak waste heat during accelerations. Mass and cost constraints for TE systems simulated were on the order of 50 kg/kW and $150/kW to capture ~1.5% fuel savings in the near-term and ~2.9% fuel savings in the future.
Cold starts, repeated engine starts, and cold temperature operation, none of which were explored in the present study, can be expected to negate some of this benefit."

All very interesting. But as far as I know, neither of the latter two is
available.

12-19-2009, 08:20 AM	#39 (permalink)
Rokeby Gen II Prianista Join Date: Jul 2009 Location: Ballamer, Merlin Posts: 453 Thanks: 201 Thanked 146 Times in 89 Posts	Piwoslaw, A very interesting thread that is bump-worthy. A Prius driver seriously interested in keeping MPGs up in the colder months soon comes to understand that in large part any efforts will hinge on retaining heat in the ICE and catalytic converter. Getting to the most efficient operating regime, S4, depends on getting the two up to temp, and in stop and go driving at least, the HSD computers will restart the ICE as it needs to keep temps up whether you like it or not. Thinking about any heat (= fuel = $$) that leaks off into the cold, cruel world is frustrating. There are a number of threads here on passive ways to retain what little heat the ICE puts off: grill blocks, pre-start-up block heaters, engine blankets, etc. All good stuff. Still, sitting at a traffic stop in the windy cold, ICE-off, with the block temps dropping rapidly (ScanGauge readout), I see the ICE kicking on apparently only to warm up the ICE or CC arbitrarily at ~145 degF, ~135 degF, and always if temps get as low as 110 degF. You wonder, Where the heck did all the BTUs go? Out the proverbial window of course. Back on target: Here is a link to some pictures of the GEN III exhaust heat recovery hardware. (Thank you, Bob Wilson.) Not great, but a start: Detroit Auto Show and Prius 2010 A little farther afield, here is a plan to recover Prius exhaust heat with a small steam turbine generator: Steam-Hybrid Prius I see that this system is "total loss" as regards the water/steam. It ends up going out the exhaust pipe. I wonder what the MPGs are for the water. And finally, a proposal published in Dec. 2007 to use "theromelectrics" to turn the excess exhaust heat directly into electricity. http://www.nrel.gov/docs/fy08osti/42256.pdf "Identifying an optimal system size is challenging. Sufficient waste heat is available at highway speeds, but little is available in city driving where the effect of engine start-stop cycles is expected to reduce waste heat by 30%. As a compromise, this study sized TE generators based on the amount of waste heat available at 40 mph (64 km/hr) constant speed driving. In transient simulations, these systems were slightly undersized to capture peak waste heat during accelerations. Mass and cost constraints for TE systems simulated were on the order of 50 kg/kW and $150/kW to capture ~1.5% fuel savings in the near-term and ~2.9% fuel savings in the future. Cold starts, repeated engine starts, and cold temperature operation, none of which were explored in the present study, can be expected to negate some of this benefit." All very interesting. But as far as I know, neither of the latter two is available. Last edited by Rokeby; 12-19-2009 at 08:50 AM..